Aharrypotter opened a new pull request, #19897:
URL: https://github.com/apache/tvm/pull/19897
## Summary
This PR fixes Relax ONNX frontend handling for integer `Div` when the divisor
is dynamic and may contain zero.
Issue #19541 reports a `SIGFPE` crash when an ONNX `Div` model has integer
inputs and the divisor is supplied as a graph input containing zero. PR
#19566
already added an import-time error for constant integer divisors containing
zero, but dynamic divisors still imported to a bare `relax.divide`. After
legalization, LLVM could still see integer `sdiv` / `udiv` with a zero
divisor.
ONNX integer division by zero is undefined. This PR keeps exact integer
division for every non-zero divisor lane, and returns zero for lanes where
the
runtime divisor is zero. The result is deterministic and avoids exposing
integer division by zero to LLVM.
## Design
### Guarded Dynamic Integer Div
For integer operands with a non-constant RHS, `Div._impl_v7` now emits a
guarded Relax subgraph:
```python
rhs_nonzero = relax.op.not_equal(rhs, relax.op.zeros_like(rhs))
safe_rhs = relax.op.where(rhs_nonzero, rhs, relax.op.ones_like(rhs))
quotient = relax.op.divide(lhs, safe_rhs)
result = relax.op.where(rhs_nonzero, quotient, relax.op.zeros_like(quotient))
```
The divisor passed to `relax.divide` is therefore never zero. The final
`where` restores the deterministic zero result for the originally-zero
divisor
lanes.
The importer normalizes the intermediate expressions whose inferred type is
needed by later `where` / `zeros_like` construction.
### Constant and Non-Integer Paths
The existing non-integer behavior is unchanged: non-integer `Div` still uses
the normal binary frontend implementation.
For integer `Div` with a constant RHS:
- constants containing zero still raise `ValueError` at import time
- constants without zero still use the normal binary frontend implementation
This keeps the PR #19566 behavior for constants while only adding runtime
guarding where import-time zero detection is impossible.
### No Float Fallback
The implementation intentionally avoids casting integer tensors through float
types. The guarded Relax graph preserves integer division semantics on all
non-zero lanes and avoids precision loss or float-to-int `inf` behavior.
### Frontend-Local Runtime Guard
This is intentionally a frontend-local runtime guard rather than a global
Relax, TIR, or LLVM integer-division policy. The check is not an import-time
Python decision for dynamic inputs; it is expressed as Relax IR and executes
with the model at runtime.
Handling this in a generic Relax/TIR pass would affect all producers of
integer
division and would need a project-wide policy for undefined integer
division-by-zero behavior: whether to trap, raise a controlled runtime error,
or return a deterministic value. This PR only addresses the ONNX frontend bug
reported in #19541 and keeps the deterministic zero result local to imported
ONNX integer `Div`.
## Updated Converter Behavior
| Case | Previous behavior | New behavior |
|---|---|---|
| integer `Div` with dynamic integer RHS | imports to bare `relax.divide`;
LLVM can see integer division by zero at runtime | imports to a guarded Relax
subgraph; non-zero divisor lanes keep exact integer division, zero-divisor
lanes return zero |
| integer `Div` with constant integer RHS containing zero | import-time
`ValueError` from PR #19566 | unchanged |
| integer `Div` with constant integer RHS without zero | normal binary
lowering | unchanged |
| non-integer `Div` | normal binary lowering | unchanged |
## Safety Checks
- Constant integer divisors containing zero raise
`ValueError("ONNX Div with integer inputs encountered divisor value 0.")`.
- Dynamic integer divisors are replaced with `ones_like(rhs)` only for the
division operand when the divisor lane is zero.
- Zero-divisor lanes are overwritten with `zeros_like(quotient)` after the
division.
- The guarded graph is asserted with structural Relax IR tests, so the
frontend
cannot silently regress to a bare `relax.divide` or wire the guard operands
incorrectly.
## Out of Scope / Non-Goals
- This PR does not define global Relax, TIR, or LLVM integer division-by-zero
semantics.
- This PR does not use a float-cast fallback for integer division.
- This PR does not change ONNX `Div` floating-point behavior.
- This PR does not change other frontends or other ONNX operators.
## Tests
The tests primarily lock the imported Relax graph shape, with one minimal VM
runtime smoke test for the original execution-time crash path.
| Test | Coverage |
|---|---|
| `test_div_integer_constant_zero_divisor_raises_valueerror` | keeps PR
#19566 constant-zero import-time error |
| `test_div_integer_dynamic_zero_divisor_runtime` | runs one dynamic INT32
ONNX `Div` model through `DecomposeOpsForInference`, `LegalizeOps`, LLVM
compile, and VM execution; asserts dtype, shape, exact non-zero divisor
results, and deterministic zero results for zero-divisor lanes |
| `test_div_integer_dynamic_zero_divisor_ir_guard` | uses
`tvm.ir.assert_structural_equal` to lock the exact guarded Relax subgraph
before legalization |
| `test_div_integer_dynamic_zero_divisor_broadcast_ir_guard` | uses
`tvm.ir.assert_structural_equal` to lock the guarded Relax subgraph when RHS
broadcasting is required |
Local validation:
```bash
python -m pytest \
tests/python/relax/test_frontend_onnx.py::test_div_integer_dynamic_zero_divisor_runtime
\
-xvs
python -m pytest tests/python/relax/test_frontend_onnx.py -k "div" -xvs
python -m ruff check \
python/tvm/relax/frontend/onnx/onnx_frontend.py \
tests/python/relax/test_frontend_onnx.py
```
Result:
```text
test_div_integer_dynamic_zero_divisor_runtime: passed
test_frontend_onnx.py -k "div": 7 passed
ruff check: All checks passed
```
## References
- Closes [#19541](https://github.com/apache/tvm/issues/19541): ONNX integer
`Div` with a dynamic zero divisor can crash at runtime.
- Follows up PR #19566: previous constant-zero divisor import-time error.
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